Drive point for explosive charge

ABSTRACT

A hollow plastic drive point for connection to the end of a cylindrical explosive charge prior to depositing the charge in a drill hole. The drive point is in the form of an integrally moulded body providing a conical forward portion and an openended rear portion defining a cylindrical inner surface for engaging the charge as the drive point is slid over the end of the charge so as to frictionally hold the drive point on the charge.

States Patet Stanley T. Graham;

Gordon Robert Rintoul, both of Calgary, Alberta, Canada Dec. 26, 1968 Aug. 17, 1971 Ace Explosives Ltd.

Alberta, Canada Inventors App]. No. Filed Patented Assignee DRIVE POINT FOR EXPLOSIVE CHARGE 3 Claims, 2 Drawing Figs.

US. Cl l02/2L8, 102/22 Int. Cl ..E21b 43/26, F42b 3/00, F42c 3/00 Field of Search 102/20,

References Cited UNITED STATES PATENTS 2,865,290 12/1958 Bonsper 102/22 3,150,590 9/1964 Silverman l02/2l.6 3,280,742 10/1966 Babb 102/21.8

Primary Examiner-Verlin R. Pendegrass Attorney-Weir, Marshall, MacRae & Lamb ABSTRACT: A hollow plastic drive point for connection to the end of a cylindrical explosive charge prior to depositing the charge in a drill hole. The drive point is in the form of an integrally moulded body providing a conical forward portion and an open-ended rear portion defining a cylindrical inner surface for engaging the charge as the drive point is slid over the end of the charge so as to frictionally hold the drive point on the charge.

PATE NTEU AUG] 7 I97! 599' 567 INVENTOR 6pm AM (5. ZOBEZT ZNTOUL PATEN NT DRIVE POINT FOR EXPLOSIVE CHARGE BACKGROUND OF THE INVENTION In making geophysical surveys, drill holes in the ground, which are commonly known as shotholes, are loaded with explosives which are detonated to provide shock waves. Also during excavation work, drill holes are loaded with explosives and detonated for the purpose of breaking up layers of rock. Various methods of lowering the explosives have been developed. One method involves securing a protective and guiding element on the end of the individual cylindrical explosive charge which is then dropped into the drill hole.

It is an object of the present invention to provide an economical and safe element which may be readily attached to the charge.

SUMMARY According to the present invention, there is provided a drive point for connection to the charge, the drive point being in the form of a hollow plastic body which has a conical forward portion formed integrally with a cylindrical rear portion, the rear portion defining a cylindrical inner surface for frictionally receiving the charge and holding the drive point on the charge. By forming the body of plastic, instead of metal, as has been done in various known forms, the danger of producing a spark and accidentally detonating the charge when the metal contacts the explosive or surrounding material in the shothole such as rocks, sand or gravel, is eliminated.

Preferably, the conical portion is provided with a plurality of openings so that as the charge is submerged in a drill hole the air in the drive point can escape and the water and mud can freely enter the drive point and thereby reduce the buoyancy of the charge.

In a specific embodiment of the invention, a plurality of flexible wing members are moulded integrally with the cylindrical portion of the drive point, the wing members projecting radially from the body. As the charge travels into the drill hole, contact of the wing members with the wall of the drill hole flexes the wing members rearwardly, and after the charge comes to a stop at the required depth in the drill holes, engagement' of the rearwardly inclined wing members with the wall prevents the natural buoyancy of the charge from floating it back to the surface of the water in the drill hole. Moreover, the flexed wing members retain the charge in a centered position in the drill hole.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, which illustrate the present invention by way of example:

FIG. 1 is a perspective side view of the drive point, with a portion removed for the sake of clarity; and

FIG. 2 is a bottom view of the drive point.

DESCRIPTION OF PREFERRED EMBODIMENTS The reference numeral generally denotesthe drive point of the present invention, the drive point 10 being produced in any appropriate size to fit a specific size of a cylindrical explosive charge 11 of the type commonly used for detonation in a drill hole such as those commonly called shotholes which are utilized in geophysical work. The drive point 10 is in the form of an integrally moulded thin-walled body having a forward conical portion 12 and a rear cylindrical portion 13. The conical portion 12 merges with the forward end of the cylindrical portion 13, and the cylindrical portion 13 is open at the. rear end thereof for reception of the end of the charge 11. Formed integrally with the cylindrical portion 13 is a pair of wing members 14 which project radially from cylindrical portion 13.

The entire body with the wing members is moulded as a single unit of a durable tough plastic, such as polyethylene or similar resins, and preferably the material forming the body is treated with antistatic agents which are well known in the art.

1 the charge 11 which consists of the explosive material, which may be spirally wrapped in heavy paper, as shown in the drawings, or otherwise covered with other material such as a 5 plastic coating. Accordingly, the cylindrical portion 13 defines an inner surface 15 for close. reception of the outer cylindrical surface of the end of the charge so that as the drive point is slid over the end of the charge the inner surface 15 frictionally engages the charge and provides resistance against withdrawal. In addition, there may be provided a plurality of circumferentially spaced prominences 16 on the inner surface 15, which prominences have forwardly projecting points 17 which provide small barbs. Thus, any forward pull on the drive point relative to the charge causes the barbs to dig into the paper cover of the charge, and further resist accidental withdrawal of the charge from the drive point.

Immediately within the rim of the conical portion 12, there is formed a plurality of openings 20, which are provided to allow the free entry of water and mud into the body as the charge is submerged in a drill hole. The entry of the water and air prevents the charge from returning to the surface of the water as a result of the buoyancy of the charge and the upward flow of water. The axes of the openings 20 are parallel to the longitudinal axis of the body, which arrangement simplifies the moulded process of the drive point. Although four equally evenly spaced openings are illustrated, a larger or smaller number may be utilized. Again to simplify the moulding process the number of the prominences may equal the number of openings for the prominences aligned with the openings in the longitudinal direction of the body.

Although a pair of diametrically opposed wing members is shown in the illustrated embodiment, a larger number may be provided. The wing members are of thin cross section providing flat front and rear surfaces 21 and 22. The front surface 21 is provided with a longitudinally extending rib 23 for increasing the rigidity of the wing members, and the rib may terminate at the inner ends of the wing members short of the cylindrical portion 13 so as to encourage bending of the wing members at their inner ends. The rear surface 22 of the wing members 14 are in a common plane to the rear end of the cylindrical portion 13 also for the purpose of simplifying the moulding apparatus. The thickness of the wing members and also of the ribs may be varied from that shown depending on the desired rigidity of the wing members. Moreover, the end edge of each wing member may be rounded or pointed, instead of being straight as shown in the drawings.

It may be appreciated from the above that the drive point may be economically produced and this is a significant feature of the invention since the points are not recoverable. In spite of the simplicity of the design, the drive point may be readily and firmly applied to the bare charge without any danger of producing sparks which could cause detonation of the charge while it is being handled. The conical forward portion of the body functions as a guide as the charge falls within the drill hole, and again predetonation which could be caused by sparks generated by the contact of a metal guide with the wall of the drill hole cannot occur. When the charge enters water and mud in the drill hole, the water and mud enter the drive point freely through the plurality of openings 20 so as to reduce the buoyancy of the charge. Furthermore, the wing members 14 which are bent rearwardly against the walls prevent the charge from rising back to the surface of the water in the drill hole. The wing members fulfill the additional function of maintaining the charge in a centered position in the drill hole.

Various modifications to the described embodiments will be apparent to those skilled in the art without departing from the spirit of the invention as defined in the appending claims.

We claim:

1. A drive point for connection to an end of a cylindrical explosive charge to be deposited in a drill hole, said drive point comprising a an integrally moulded hollow body of polyethylene, said drive point including a conical section providing a forward point, a thin-walled cylindrical portion outwardly therefrom.

2. A drive point as defined in claim 1, wherein said wing members are of thin cross section defining a flat rear surface, said flat rear surface being in a common transversal plane with said open end of said cylindrical portion.

3. A drive point as defined in claim 1, wherein said wings are of thin cross section and define flat forward and rearward surfaces, and each wing member is provided with a reinforcing rib along the forward surface thereof. 

1. A drive point for connection to an end of a cylindrical explosive charge to be deposited in a drill hole, said drive point comprising a an integrally moulded hollow body of polyethylene, said drive point including a conical section providing a forward point, a thin-walled cylindrical portion merging with said conical section and extending rearwardly therefrom, said cylindrical portion being open at the rear end thereof and defining a smooth internal cylindrical surface for direct frictional engagement with said charge as said charge is forced longitudinally into the open end, a plurality of prominences integrally moulded on the internal surface, said prominences providing forwardly projecting barbs for engagement with said charge, said conical section having a plurality of circumferentially spaced openings therethrough, and at least a pair of diametrically opposed flexible wing members formed integrally with the cylindrical portion and extending outwardly therefrom.
 2. A drive point as defined in claim 1, wherein said wing members are of thin cross section defining a flat rear surface, said flat rear surface being in a common transversal plane with said open end of said cylindrical portion.
 3. A drive point as defined in claim 1, wherein said wings are of thin cross section and define flat forward and rearward surfaces, and each wing member is provided with a reinforcing rib along the forward surface thereof. 